The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the inventors hereof, to the extent the work is described in the background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present disclosure.
Image scaling is an important step in video processing and display. Images may need to be up-scaled or down-scaled by arbitrary factors for several reasons, such as to be displayed on a device with a different resolution than that of the image. Image scaling may also be required in Picture-In-Picture (PIP) applications, where an image may need to be scaled to the size of a PIP window. Image scaling may involve a change in the resolution of an image.
Changing the resolution of an image may distort the image in an undesirable manner by introducing artifacts into the image. An artifact may be an element introduced into the image by the process of scaling that was not part of the original image. For example, scaling an image from a low to a high resolution may introduce blurred edges, jagged edges, or ringing artifacts. These artifacts frequently occur near sharp transitions, or edges, in an image. In another example, scaling an image from a high to a low resolution may result in a loss of details.
Image scaling may need to be performed as a component of video processing for live video display. Image scaling may occur on control circuitry, such as application-specific integrated circuits (ASICs), which pose restrictions on memory usage for image pixels, interpolation filter coefficients, and intermediate data. The control circuitry may also require the computational complexity of the image processing algorithm to be low, or involve only fixed-point integer arithmetic.
Existing scaling methods involve scaling first in the horizontal direction, and then scaling in the vertical direction, or vice-versa. The existing methods therefore may utilize a large number of image scalers on a single chip. Such scaling methods may introduce undesirable artifacts into the scaled images. Adaptive scaling methods may reduce the artifacts introduced by scaling but typically require a large number of line buffers for each image scaler, which prohibits their usage in chips with a large number of image scalers.